[1]} suggested that much of what has been assumed to be the O i \(\) 1304 quartet could be the Si ii \(\) 1307 doublet and
that the latter could dominate in many objects. [2]} propose that typically Si ii makes up 50% of the blend. If this is the case, assuming that the observed \(\) 1304/\(\) 8446 ratio is just giving the ratio of the O i lines will result in a major underestimate of the reddening. However, such strong Si ii \(\) 1307 is a problem for emission line modelling because photoionization models cannot produce strong Si ii \(\) 1307. ([1]} refer this this as “the Si ii disaster” – see their Appendix C). We will nevertheless investigate the question of possible Si ii contamination in Section 5.2.
